1. Field of the Invention
The present invention relates to a disk drive control method, a disk drive, and a write control circuit, and particularly, to a disk drive control method, a disk drive, and a write control circuit able to prevent write operations when floating height of a head is abnormal.
2. Description of the Related Art
Magnetic disk drives, such as hard disk drives (HDDs) are widely used in computers as storage media. The HDD includes a magnetic disk, a magnetic head for reading data from or writing data into the magnetic disk, and an actuator for holding a slider on which the magnetic head is fixed.
The actuator is driven by a voice coil motor (VCM) to rotate, and due to the rotation of the actuator, the magnetic head is driven to move in the radial directions on the magnetic disk; thereby, the magnetic head is driven to be able to access any place on the magnetic disk to read data from or write data into the magnetic disk.
A suspension is provided at the front end of the actuator, and the slider is fixed on the suspension. The slider has a surface facing the magnetic disk, which is called an “ABS” (Air Bearing Surface)”. When the magnetic disk is rotating, an air flow occurs between the ABS and the magnetic disk, and the slider flies relative to the magnetic disk. In this state, the distance between the magnetic head and the magnetic disk (it is referred to as “floating height”) is stable at a position where the force from the actuator and a lifting force due to the air flow are in balance.
In HDDs fabricated in recent years, along with increased recording density of the HDDs, the floating height tends to be small. For this reason, the floating height of the magnetic head may become unstable because of presence of contamination, or non-uniformity of a lubricant on the surface on the recording medium, or changes of the shape of the magnetic head caused by a writing current when writing data in the magnetic disk, so that the floating height may vibrate periodically. If writing data in the magnetic disk under this condition, the distance between the magnetic head and the magnetic disk lengthens, a writing magnetic field becomes weak, and consequently, it is difficult to correctly write data in the magnetic disk.
In order to prevent such a write error, for example, Japanese Laid-Open Patent Application No. 9-139040 (hereinafter, referred to as “reference 1”) discloses a technique in which variation of the floating height of the magnetic head is monitored by an AGC voltage from an AGC circuit serving as a data reproduction processing circuit for receiving a reproduction signal obtained when the magnetic head reads data from the magnetic disk and for performing data reproduction processing. A CPU compares the input AGC voltage to threshold data DT stored in a memory, and outputs a flying variation detection signal FS indicating the floating height of the magnetic head varies abnormally when the floating height of the magnetic head is outside of a specified range.
In the technique disclosed in reference 1, however, since the floating height variation of the magnetic head is monitored by comparing the reproduction signal to a threshold value, it is difficult to precisely detect the floating height variation of the magnetic head.
Specifically, in the related art, a single threshold value is used to detect the floating height variation of the magnetic head over the entire area of the magnetic disk. For example, as mentioned above, when contamination or a lubricant is present on the surface on the recording medium, local projecting regions exist on the magnetic disk. If the threshold value happens to be set with one of the projecting regions as a reference, it is difficult to obtain correct detection results in other regions of the magnetic disk.